Variable resistor device

ABSTRACT

A variable resistor device comprising a housing formed by walls, one of which is provided with a resistive material on its inner surface, a rotatable screw shaft mounted in the housing for elongating along the resistive material on the inner surface of the wall and a movable contact having a portion for coming in contact with the resistive material and a portion for engaging with the screw thread of the screw shaft to be shifted in contact with the resistive material by the rotation of the screw shaft, whereby the variable resistance is obtained between one end of the resistive material and the screw shaft.

United States Patent- [1 1 Kitamura et al.

[451 Feb. 25, 1975 VARIABLE RESISTOR DEVICE [75] Inventors: NobuoKitamura, Sagamihara;

Miroshi Fukagawa, Tokonama, both of Japan [30] Foreign ApplicationPriority Data 3,665,364 5/1972 Maurice 338/180 3,732,520 5/1973VanBenthuysen et al.. 338/180 3,742,421 6/1973 Rooijen 338/180 PrimaryExaminer-Bruce A. Reynolds Attorney, Agent, or Firm-Lewis H. Eslinger;Alvin Sinderbrand 57 ABSTRACT A variable resistor device comprising ahousing formed by walls, one of which is provided with a resistivematerial on its inner surface, a rotatable screw shaft mounted in thehousing for elongating along the resistive material on the inner surfaceof the wall and a movable contact having a portion for coming in contactwith the resistive material and a portion for engaging with the screwthread of the screw shaft to be shifted in contact with the resistivematerial by the rotation of the screw shaft, whereby the variableresistance is obtained between one end of the resistive material and thescrew shaft.

3 Claims, 11 Drawing Figures PATENTEUFEBZSISYS ya+a VARIABLE RESISTORDEVICE BACKGROUND OF THE INVENTION l Field of the Invention Thisinvention relates generally to mechanical variable. resistor devices,and more particularly to a variable resistor unit having an improvedsliding mechanism for changing the resistance value and suitable forbeing used as avoltage supplying device in voltage controlled tuners of,for example, a television receiver.

2. Description of the Prior Art There are, inrough classification, twotypes of tuners for a signal receiver, such as a television reciever,-whichis adapted to receive selectively a plurality of signalstransmitted with-different carrier frequencies, respectively. One of thetwo types is a mechanically selecting tuner in which a plurality ofresonance circuits have resonahtfrequencies corresponding to the signalsto'be selectively received, respectively, are provided and theseresonance circuits are selected by movable mechanical contacts toreceive a selected one of the transmitted signals. The other of the twotypes is a voltage controlled tuner in which a resonance circuit havinga voltage controlled variable reactance element is provided to receive aselected one of the transmitted signals by changing its resonantfrequency which can be varied by changing a voltage supplied to thevoltage controlled variable reactance element.

In general, compared with the former, the latter has an advantage thatthe movable mechanical contacts which are apt to cause troubles areeliminated. In the voltage controlled tuner, a plurality of variableresistor units are used for producing control voltages to be selectivelysupplied to the voltage controlled variable reactance element to set theresonance circuit to have a resonant frequency corresponding to theselected one of the transmitted signal. In this case, the variableresistor unit, is required to be able to vary its voltage valuecontinuouslyv in a predetermined range in order to produce severalcontrol voltages, each value of which is determined in response to thecarrier frequency of the selected signal to be received, although eachof the variable resistorunit's, is arranged to produce one of theseveralcontrol voltages inactu al use. In order to' comply with thisrequirement, a sliding mechanism for varying the resistance value isusually provided.

Various variable resistor units have been previously proposed for such ause, however, they need a number of parts and are complicated inconstruction.

OBJECT OF THE INVENTION An object of this invention is toprovide animproved variable resistor device having a simple mechanism for varyingthe resistance value therein.

Another object of this invention is to provide a compact variableresistor device which contains threin an improved slidable contact forvarying the resistance value.

Further, another object of this invention is to provide a compactvariable resistor unit suitable for being utilized as a control voltagesupplying device for a variable reactance element in a voltagecontrolled tuner.

SUMMARY OF THE INVENTION A variable resistor device of this inventionbelongs to sliding variable resistors which provides a variableresistance value in response to the position of a sliding contacttherein. In this invention, a housing formed by a plurality of walls isprovided and a resistive material is provided, for example, by coatingon the inside surface of one of the walls. In the housing, a rotatablescrew shaft is mounted and a contact which is slidable on the resistivematerial is engaged with the rotatable screw shaft to be moved incontact with the resistive material by the rotation of the screw shaft.This slidable contact is formed by a resilient conductive material, for

example, a bent metal plate and provided with an engaging portiondirectly engaging with the screw thread of the rotatable screw shaft, sothat the sliding mechanism is simple in construction and assembly, andthe wholeof the variable resistor device can be constructed BRIEFDESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of details ofone embodiment of variable resistor devices according to the presentinvention;

FIG. 2 is a plane view of the variable resistor device shown in FIG. I;

FIG. 3 is a sectional view taken along the line IIIIII in FIG. 2;

FIG. 4 is a sectional view taken along the line lVIV in FIG. 2;

FIG. 5 is a side view seen to the line VV in FIG. 2;

FIGS. 6 8 are partial views of the variable resistor device shown inFIG. 1;

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 7;

FIG. 10 is a sectional view taken along the line X-X in FIG. 7; i

FIG. 11 is-an enlarged: sectional view of that shown in FIG. 10 used forexplanation of one of featured portions of variable resistor devicesaccording to the present invention. I 7

DESCRIPTION OF THE PREFERRED EMBODIMENT cording to thisinventionconsists of an elongated housing box 2 the upper surface ofwhich is opened, a rotatable'screw shaft 3 with screw threads which islocated in the elongated housing box 2 along its longitudinal direction,a lid board or resistor board 6 which closes the opening 4 of thehousing box 2 and has a resistive material coated on its inside surfaceto form a resistor portion 5 (refer to FIG. 6), and a movable contact 7which is inserted between the rotatable screw shaft 3 and the resistorportions.

As shown in FIGS. 2 to 6, the rotatable screw shaft 3 is assembled inthe housing box 2 to pass therethrough along its longitudinal directionand is rotatably supported at its both end portions by bores 8 formed inthe side end walls of the housing box 2. A gear 9 is formed integrallywith the rotatable screw shaft 3 at its one end portion while aresilient plate 10 is insertedto the rotatable screw shaft 3 at itsother end portion to thereby prevent the rotatable screw shaft 3 fromcoming out from the housing box 2. A pair of connecting terminals 11 and12 are led out through the resistor board 6 from the both ends of theresistive material 5 on the resistor board 6 to the outside surfacethereof. Five cutouts 13 of substantially trapezoid configuration areformed on the resistor board 6 at its peripheral portion,'while fiveprojections 14 of corresponding trapezoid configuration are formed onthe upper edge of the housing box 2 at predetermined positions,respectively.

-The five trapezoid cutouts 13 formed in the resistor board 6 receivethe five corresponding trapezoid projections 14 formed on the upper edgeof the housing box 2, respectively, to close the upper opening 4 of thehousing box 2 and thus to form a housing as a whole. Aconnectingterminal 21 is provided such that its one end is electricallyconnected to the rotatable screw shaft 3 at one end thereof in thehousing box 2 and the other end of the connecting terminal 21 isprojected outwardly beyond the resistor. board 6.

As shown in FIGS. 7 to 10, themovable contact 7 consistsof a resilientconductive plate which is bent. At the topof the bent portion of themovable contact 7, it isembossed to form a pair of left and rightcontact points 15. One end 16 of the movable contact 7 is bentdownwardly with an inclination in accordance with the thread angle of ascrew thread 20 formed on the rotatable screw shaft 3, and has formed acutout 17 of substantially delta shape at'its approximately centerposition. The delta shape cutout 17 engages with the screw thread 20 oftherotatable screw shaft 3.'The movable contact 7 has formed integrallytherewith, at its other end 18, a pair of guiding portions 19 whichextend outwardly therefrom along the rotatable screw shaft 3.

The thus formed movable contact 7 is located betweenthe rotatable screwshaft 3 and the resistor portion 5 against its resiliency. Thus, thepair of contact points of the movable contact 7 engage with the resistorportion 5, the cutout 17 formed in one end 17 of the movable contact-7engages with the screw thread of therotatable screw'shaft 3 on its upperside, and the pair of guiding portions 19 formed on one end 18 of themovable contact 7 are supported by therotatable screw shaft 3 byabutment therebetween.

when the variableresistor device 1 constructed as above is employed as avoltage controlled tuner, a plurality of-the variable resistor devices 1the number of which is,-selected in accordance with that of requiredchannels are arranged. around the channel selecting shaft of a tunerwhich is intermittently moved ,with a constant pitch in'a turret-likemanner. When the knob of the tuner for selecting the channel is operatedto rotate the channel selection shaft ofthe tuner sequentially, threeconnecting terminals 11, 12 and 21 of the selected variable'resistordevice are sequentially connected to a spring contact provided in thetuner proper to apply to, for example, a variable capacitor diode, whichforms a receiving resonance circuit, a control voltage to enable thevariable capacitor diode to have such a capacity as can receive adesired channel signal.

In this case, if afine adjusting knob is rotated, a fine adjustmentdriving gear which is rotated in ganged relation with the fine adjustingknob meshes with the gear 9'attached to the rotatable screw shaft 3 ofthe variable resistor device 1 which corresponds to the received channeland is connected to the resonance circuit formed by the variablecapacitor diode through three connecting terminals 11, 12 and 21 andspring contact. Thus, the gear 9 is rotated, the. movable contact 7 ismoved, and the contact points 15 slide on the resistor portion 5, sothat the resistance value of the variable resistor device 1 isfine-adjusted to provide a predetermined control voltage for thevariable capacitor diode for the received channel between the connectingterminals 11 and 21 or 12 and 21. ln other words, when the rotatablescrew shaft 3 is rotated and adjusted by the gear 9, the movable contact7, which engages at its end 16 with the screw thread 20 of the rotatablescrew shaft 3, is adjusted to slide on the resistor portion 5 inaccordance with the rotation of the rotatable screw shaft 3. In responseto the, adjustment of the movable contact 7, the contact position of thecontact points 15 is adjusted relative to the resistor portion 5 toachieve the fine adjustment of the resistance value between theconnecting terminals 11 and 2] or between the connecting terminals 12and 21.

The other end 18 of the movable contact 7 contacts with the uppersurface of the rotatable screw shaft 3 through the pair of guidingportions 19. in other words, the guiding portions 19 do not engage withthe screw thread 20 of the rotatable screw shaft 3 but only contact withthe upper surface of the rotatable screw shaft 3 in a manner of grippingthe latter. Accordingly, the deviation of the movable contact 7 from therotatable screw shaft 3-to the left and right directions is prevented byboth the guiding portions 19. That is, the two guiding portions 19 actto prevent the movable contact 7 from coming off the rotatable screwshaft 3 and to guide the former along the latter smoothly during theadjustment of the movable contact 7.

In this case, as shown in FIG. 11, the movable contact 7, the rotatablescrew shaft 3 and the resistor board 6 have the following dynamicalconstruction. That is to say, both the contact points 15 aresymmetrically arranged at distances of a and a, which are approximatelyequal with each other, with respect to the center axis Y-Y which passesthrough the center of the rotatable screw shaft 3 and is perpendicularto the resistor board 6, so that the movable contact 7 is set at astable position on the rotatable screw shaft 3 by forces F and F exertedon the contact points 15 causedby the resiliency (spring force) of themovable contact 7 itself and the guiding portions 19. As a result, themovable contact 7 can, slide'between the resistor portion Sand therotatable screw shaft'3 without meandering to provide a stable controlvoltage, if there is no eccentricity in the rotatable screw shaft 3. Inpractice, a distance b between the center axis of the rotatable screwshaft 3 and the resistor board 6 is selected as small aspossible soas tomake the contact points 15 stable as possible with respect to theresistor portion 5.

As described above, with this invention the movable contact is formed ofthe conductive plate with resiliency, which is bent, and at least oneend of the movable contact is made to engage with the rotatable screwshaft to move the movable contact by the vrotatable screw shaftincontact ,with the resistor portion, so that with resistive material onthe inner surface thereof,

said one wall further being provided with at least one electricalterminal connected to said resistive material;

a screw shaft longitudinally mounted in said housing and rotatablysupported by said end walls, said screw shaft having threads and beingmade of conductive material;

a second electrical terminal disposed at one end of said screw shaft andin electrical contact therewith,

1 said second electrical terminal extending externally of said housing;and

a movable contact element positioned on said screw shaft andbidirectionally advanced along said screw shaft in accordance with therotation thereof, said contact element being formed of a resilientconductive plate bent between end portions thereof to thereby form acontact portion which is resiliently urged into physical contact withsaid resistive material, one end of said movable contact element beingbent into engagement with said screw shaft at an inclination inaccordance with the thread angle of said screw threads and being formedof a V-shaped cutout, and the other end of said movable contact elementhaving a pair of guiding portions formed integrally therewith whichextend outwardly along said screw shaft so as to not engage with thescrew threads but to be supported by said screw shaft by abutmenttherebetween. 2. A variable resistor device in accordance with claim 1wherein said contact portion of said movable contact element is embossedto form a plurality of contact points which are in physical contact withsaid resistive material.

3. A variable resistor device in accordance with claim 1 wherein one endof said screw shaft is provided with a gear to receive a driving gear inmeshing engagement therewith to thereby rotate said screw shaft.

1. A variable resistor device, comprising: a housing formed of wallsincluding end walls, one of said walls being detachable and beingprovided with resistive material on the inner surface thereof, said onewall further being provided with at least one electrical terminalconnected to said resistive material; a screw shaft longitudinallymounted in said housing and rotatably supported by said end walls, saidscrew shaft having threads and being made of conductive material; asecond electrical terminal disposed at one end of said screw shaft andin electrical contact therewith, said second electrical terminalextending externally of said housing; and a movable contact elementpositioned on said screw shaft and bidirectionally advanced along saidscrew shaft in accordance with the rotation thereof, Said contactelement being formed of a resilient conductive plate bent between endportions thereof to thereby form a contact portion which is resilientlyurged into physical contact with said resistive material, one end ofsaid movable contact element being bent into engagement with said screwshaft at an inclination in accordance with the thread angle of saidscrew threads and being formed of a Vshaped cutout, and the other end ofsaid movable contact element having a pair of guiding portions formedintegrally therewith which extend outwardly along said screw shaft so asto not engage with the screw threads but to be supported by said screwshaft by abutment therebetween.
 2. A variable resistor device inaccordance with claim 1 wherein said contact portion of said movablecontact element is embossed to form a plurality of contact points whichare in physical contact with said resistive material.
 3. A variableresistor device in accordance with claim 1 wherein one end of said screwshaft is provided with a gear to receive a driving gear in meshingengagement therewith to thereby rotate said screw shaft.